Erick Tukuniata (erickblender) renamed this task from Pose bone: clearing a transformations in pose mode does not the mirrored bones even when the X-axis mirror is activated. to Pose bone: clearing transformations in pose mode does not affect the mirrored bones even when the X-axis mirror is activated..Wed, May 20, 7:15 PM

Did you moved the bone first?
I see, i was not clear, it is Alt+R that should clear since bones are auto-IK, Alt+G doesn't anything here as well. This is just my old habit when i clear i clear everything.
So after you moved the bone (in the given .blend file), select all .L bones then Alt+R.
Sorry for that.

The mirror transformation into pose mode is a specific feature of the transform operators.
So operators like POSE_OT_rot_clear will not affect mirrored bones.
We could think of something like D6736 and use a common function to update the mirror on different operators.

I am not sure if we can consider this an bug/error, but I will confirm it as a bug for now.